A UV cover is a strip of sun-resistant fabric sewn along the leech and foot of a roller-furling headsail, or occasionally a furling mainsail, so that when the sail is rolled away the cover is on the outside and the sailcloth is protected from sunlight. It is also called a sacrificial strip or sun cover, and that first name says exactly what it is for: it takes the ultraviolet punishment so the sail does not. For a beginner, the UV cover is the coloured band on the edge of a furled genoa. For a sailmaker it is the single most important factor in how long a furling sail lasts, because UV degradation, not sailing, is what kills most cruising headsails.
Why sailcloth needs protecting
Ultraviolet light breaks the molecular chains in synthetic fibres. Polyester (Dacron) resists it reasonably well, nylon poorly, and many high-modulus fibres used in laminates, such as aramids like Kevlar, very poorly indeed. Mylar film and the adhesives in a laminate also weaken with UV exposure, and the first sign is often a leech that has gone brittle and cracks along the folds. Sunlight is strongest on the thread: stitching sits proud of the cloth and takes the full dose, so a sail can look sound while its seams are ready to let go. Rolled on a furler, a headsail presents the same narrow band of leech and foot to the sun every day for months, and without a cover that band is destroyed while the rest of the sail is like new.
What a UV cover is made of
- Acrylic canvas: solution-dyed acrylic such as Sunbrella is the standard for cruising sails. It is heavy, very UV-stable, comes in colours to match the sprayhood and dodger, and typically outlasts the sail it protects. Its weight and stiffness cost a little in light-air performance and make the furled sail bulkier.
- UV-treated polyester: a lighter sailcloth with a UV inhibitor coating, often in white or a pale grey. It is lighter and less bulky than acrylic, better for performance-minded cruisers and club racers, but it has a shorter life and needs replacing more often.
- UV-resistant laminate strips: on some racing and performance cruising headsails, a light film or taffeta strip with UV inhibitors is used where minimum weight matters.
How a UV cover affects the sail
A sailmaker has to design around the cover. An acrylic strip on the leech adds weight and stiffness exactly where a headsail should be lightest, so the leech tends to hook a little in light air and the sail needs a slightly firmer leech line arrangement. The extra layer changes how the sail rolls: the leech and foot are thicker than the body, so the rolled sail has a shape that affects how well the partly-reefed sail sets. And the cover must be on the correct side. A furler that rolls the sail clockwise from behind needs the cover on the port side of the sail, and the other way round for anticlockwise. Ordering a new sail or a new furler without checking the direction is a common and expensive mistake.
Maintenance and replacement
Inspect the cover every season. The stitching goes first: run a thumbnail along the seams and if the thread breaks or powders, it is time to restitch. Fading and thinning of the fabric itself follow. An acrylic cover can usually be restitched two or three times before it needs replacing, and replacing the cover is a routine loft job that costs a fraction of a new sail. Leave a failing cover too long and the leech tape and the leech line beneath it start to go, and the repair becomes a rebuild. Always furl the sail tightly and fully, with the cover completely covering the roll, and take a few turns of the sheets around the furled sail to stop it unrolling in a gale.
Frequently Asked Questions about UV Cover
How long does a UV cover last?
An acrylic cover typically lasts five to ten years in temperate climates and rather less in the tropics, with restitching every few seasons. UV-treated polyester covers last roughly half as long.
Does a UV cover slow the boat down?
Slightly. The extra weight and stiffness on the leech cost a little in light air and can make the leech hook. A lighter polyester or laminate strip reduces the penalty at the cost of durability.
Which side of the sail does the UV cover go on?
Whichever side ends up outside when the sail is furled, which depends on the direction your furler rolls. Check before ordering; the cover cannot be moved to the other side without unpicking it.
The UV cover asks nothing of the sailor except a check each spring and a tight furl each evening, and in return it doubles or trebles the life of the most-used sail on a cruising boat. Choose the material to suit how you sail, get the side right, keep the stitching sound, and the genoa beneath it will still be setting well long after an unprotected one would have been consigned to the skip.